President Donald Trump has decided to pull the United States out of the landmark 2015 Paris Climate Accord.

"We're getting out," Trump said in a White House statement.

Trump said he made the decision because the accord is "very unfair at the highest level to the American people." The U.S. will stop honoring non-binding parts of the agreement "as of today" Trump said.

Earlier in the day, at a photo session with visiting Vietnamese Prime Minister Nguyen Xuan Phuc, Trump said he was hearing from “a lot of people both ways” as he considered his options.

Spokesman Sean Spicer said those consulted include U.S. business leaders and foreign heads of states.

News of the pending decision was greeted with howls of derision in the environmental community, and the mayors of the largest U.S. cities vowed to remain faithful to the accord, regardless of what Trump decides.

New York Mayor Bill de Blasio’s Tweet read: “We'll take matters into our own hands. I plan to sign an executive order maintaining New York City’s commitment to the Paris Agreement.”

Climate change activists were predictably furious, assuming that the decision would go against their interests.

"Donald Trump has made a historic mistake, which our grandchildren will look back on with stunned dismay at how a world leader could be so divorced from reality and morality,” Sierra Club President Michael Brune said in a statement emailed to VOA.

A similar statement from the League of Conservation Voters read, “With this wildly irresponsible decision, President Trump would not only [be] jeopardizing the health and safety of American communities, but also undermines the United States’ position of global leadership on a host of issues.”

Billionaire entrepreneur Elon Musk, the founder of Space X, threatened to resign from the three White House scientific advisory boards if the president actually withdraws from the accord. He tweeted, “Will have no choice but to depart councils in that case.”

Economist Gary Hufbauer of the Washington-based Peterson Institute told VOA he expects other countries to remain a part of the accord, and that Trump deciding to leave would "put the U.S. in a bad light."

"A statement by President Trump that the U.S. is leaving the Paris accord doesn’t really trigger any enforcement action by other countries, and probably is more of a declaration of intent than an actual leaving of the accord," he said.

The pending decision also prompted worried reactions from European and other allies.

Russian presidential spokesman Dmitry Peskov said the agreement has great significance, but will be less effective without its key participants.

Chinese Premier Li Keqiang said China will stand by its commitment to implement the deal.

The United Nations' official Twitter account carried this message: “Climate change is undeniable. Climate action is unstoppable. Climate solutions provide opportunities that are unmatchable.”

France’s ambassador to the United States, Gerard Araud, tweeted, “Major U.S. corporations have expressed their support of the Paris accord.”

European Commission President Jean-Claude Juncker said President Donald Trump doesn't "comprehensively understand'' the terms of the Paris accord. Juncker says European leaders tried to explain the process for withdrawing from the global agreement to Trump "in clear, simple sentences'' during meetings last week.

Juncker, who was among the leaders Trump met with last week, notes that it takes several years to pull out of new international treaties. "This notion, `I am Trump, I am American, America first and I am getting out,' that is not going to happen,'' he said.

Not all reaction has been negative, though.

A group of 22 Republican senators issued a letter last week, urging Trump to “make a clean break from the Paris agreement.” The letter argued that “remaining in it would subject the United States to significant litigation risk” that could complicate Trump’s effort to overturn Obama era regulations, known as the Clean Power Plan.

Freedom Works, an organization dedicated to the principle of smaller government, argued in a statement that adhering to the agreement would be too expensive, costing the U.S. economy more than $2 trillion and nearly 400,000 jobs.

“Americans haven’t seen real economic and wage growth for far too long, and this misguided treaty failed to strike anything close to a balance between preserving the environment and prosperity,” the statement said.

Brett Schaefer of the pro-Trump Heritage Foundation said the decision to pull out of the Paris Accord should be an easy one for Trump, who was elected after calling climate change “a hoax.”

“If you pull out, you are going to get criticism from environmental groups and others on the political left that probably don’t support you anyway,” Schaefer said. “But to avoid that criticism you would impose higher costs on American voters, American consumers, American businesses, retard U.S. economic growth going forward, and break a campaign promise.

That is about as black and white as can be, and I think the choice should be pretty clear to the president,” Schaefer said.